Heat concentrating device and firing method

ABSTRACT

A heat concentrating device particular useful for firing objects formed of metal clay includes a preferably frusto-conical body with a hollow interior surrounded by a continuous sidewall, a wide lower end or base, a relatively narrow upper end, a support screen disposed across the upper end for supporting objects to be fired, and an aperture adjacent the upper end for insertion of a temperature sensor connected to a pyrometer assembly for monitoring the temperature at the upper end of the body. The device is placed over a stove burner to capture the heat emitted by the burner in the interior of the body and concentrate the heat at the upper end of the body so as to heat objects placed on the support screen to a suitable firing temperature.

RELATED APPLICATION DATA

This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/676,654, filed Apr. 29, 2005, titled “Heat Concentrating Firing Cone”.

FIELD OF THE INVENTION

The present invention generally relates to heating apparatus and devices, and in its preferred embodiments more specifically relates to a device for concentrating the heat emitted by a stove burner for the purpose of firing objects formed of or in combination with metal clay, and to a method of firing objects utilizing the device of the invention.

BACKGROUND OF THE INVENTION

A material known as metal clay is becoming increasingly popular for use in making jewelry, small sculptures, and other types of relatively small objects of precious metal, particularly silver but also including gold. The metal clay material itself is finely powdered metal mixed with an organic binder and water to form a malleable clay-like substance. This clay can be shaped and formed in many ways to create objects. A created object is then heated to first burn off the organic binder and then fuse the metallic particles together, in a process known as sintering. The final result of the heating or sintering process is the creation of an object of silver metal.

The fusing of the metal particles can occur at temperatures as low as 1110 degrees Fahrenheit if the object is held at that temperature for approximately 45 minutes. Best results and greatest strength of the completed object can be achieved if it is heated to approximately 1650 degrees Fahrenheit and held at that temperature for approximately 2 hours. Metal clays are available in different compositions, each formulated to be heated or fired at a particular temperature. The most important factor in the successful completion of the creation of a metallic object from metal clay is the firing process. If the firing temperature is too low the metal particles will not properly fuse and the desired strength and integrity will not be achieved. If the firing temperature is too high metal particles will fully melt and flow, destroying the shape of the object.

Several approaches to firing metal clay objects are known in the prior art, all of which are effective when properly used, but each of which suffers from certain disadvantages. One approach is to fire the objects in a kiln, typically electrically heated. With a kiln the firing temperature can be controlled and very good results can be consistently obtained. Kilns are, however, costly to purchase, ranging in price up to $1,200.00 or more. Further, the firing process in a kiln is time consuming. The object or objects to be fired are placed in a cool kiln, the kiln is closed and brought up to the selected temperature and maintained at that temperature for a selected period of time, and then allowed to cool before the kiln is opened and the fired objects removed for inspection. In most kilns the objects cannot be inspected during the firing process, since the kiln must remain closed.

In another approach metal clay objects may be fired using a hand held torch. A torch will bring a metal clay object to the necessary temperatures for the firing process, but the torch must be very carefully controlled during the entire process to achieve successful results, and a significant level of skill is required. The torch must be continuously moved during the entire firing process, which becomes impractical at higher temperatures and longer firing times. The mass of a metal clay object that can be effectively fired using a torch is also limited; generally considered to be about 20 grams. Further, precise temperature control is not possible.

Another approach utilizes what is commonly referred to as a “hot pot”; an apparatus that uses a marine fuel gel as a heat source to fire metal clay objects placed within the pot. The firing continues until the fuel is exhausted and the hot pot is then preferably allowed to cool before the fired object is removed. The fuel combustion is not controllable, and the firing temperature cannot be controlled. Further the mass of a metal clay object or combination of objects that can be fired in a hot pot is limited, also to about 20 grams.

There remains a need for an approach for the firing of, particularly, metal clay objects utilizing a device that is inexpensive to obtain and use, that allows control of the firing temperature, that allows inspection of the object or objects during the firing process, that does not require significant skill to use, that allows larger objects or a plurality of objects to be fired at the same time, and that provides consistently satisfactory results.

SUMMARY OF THE INVENTION

The present invention provides a device for firing metal clay objects that is designed to be used with a conventional butane or propane fueled burner, such as but not necessarily limited to a camp stove, to concentrate the heat emitted by the burner and raise the temperature at the firing zone located above the burner to the necessary temperature for firing metal clay objects. The present invention also provides a method of firing metal clay objects utilizing the device of the invention.

In its preferred embodiments the device of the invention comprises a frusto-conical body formed of a non-combustible insulating material, to be placed over the burner of a stove used as a heat source with the wider end of the body nearest the burner and the narrower end farther from the burner. A support screen is disposed at the narrower, upper end of the body to support objects placed on the support screen. It is preferred that the body be penetrated by an aperture adjacent to the narrower end for insertion of a temperature probe for monitoring the temperate in the firing zone.

The method of the invention includes the basic steps of placing the device of the invention on a suitable stove, placing the metal clay object or objects to be fired on the support screen, igniting the stove burner, monitoring the temperature within the firing zone, adjusting the burner to maintain the desired firing temperature for the desired firing time, extinguishing the burner, and removing the completed objects from the support screen.

Advantages provided by the device and the method of the invention, and objectives achieved by the device and method of the invention include the following:

-   -   heats to effective temperatures for firing metal clays;     -   enables accurate temperature control when used with a pyrometer;     -   allows the firing of a relatively large mass of metal clay,         which may occupy up to approximately 80% of the surface area of         the support screen, up to approximately 100 grams of metal clay;     -   is completely portable, requiring no electricity     -   uses a common economical fuel source found almost anywhere in         the world     -   is capable of firing metal clays and combinations of metal clays         and ceramic beads; and     -   allows a user to fire enamels and see the results right away.

The device of the invention and the method of the invention will be described in detail below, with reference to the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation view of the preferred embodiment of the device of the invention.

FIG. 2 is a top plan view of the preferred embodiment of the device of the invention, without a support screen in place.

FIG. 3 is a top plan view of the preferred embodiment of the device of the invention, with a support screen in place.

FIG. 4 is a bottom plan view of the preferred embodiment of the device of the invention, without a support screen in place.

FIG. 5 is a sectioned side elevation view of the preferred embodiment of the device of the invention, without the support screen in place, along line 5-5 of FIG. 2.

FIG. 6 is a side elevation view of the preferred embodiment of the device of the invention in place upon an illustrative stove burner, with a pyrometer assembly for monitoring temperature.

DESCRIPTION OF THE INVENTION

In the preferred embodiment the heat concentrating device of the invention, generally designated by reference number 10, is formed as a hollow frusto-conical body 11 with a continuous sidewall 12, a narrow first or upper end 13, and a wide second or bottom end or base 14. Sidewall 12 has an inner surface 15 and an outer surface 16. The plane defined by the upper end of the body and the plane defined by the lower end of the body are parallel to each other, and perpendicular to the axis of body 11.

An annular ledge 17 is formed in upper end 13 of body 11, extending from the inner surface 15 of the body toward the outer surface of the body, leaving a lip 18 between ledge 17 and the outer surface of the body. A supporting means 19, preferably formed as a grid or screen, is removably disposed on ledge 17 and extends across the hollow interior of body 11 at its upper end, to support objects to be fired using the device of the invention.

Sidewall 12 is penetrated by an aperture 20 extending fully through the sidewall between outer surface 16 and inner surface 15, to receive a temperature sensor 21 therethrough. Aperture 20 is disposed slightly below ledge 17, so that a temperature sensor inserted through the aperture will be positioned immediately below support screen 19 without contacting the support screen and will provide a temperature reading in the immediate vicinity of objects placed on the support screen without interfering with those objects.

Lower end 14 of sidewall 12 is to be received upon the supporting structure surrounding the burner of a stove with which the device is used. A typical stove of the type with which it is contemplated that the device will be used includes a supporting structure with horizontal supports symmetrically disposed around and extending outwardly from the burner, and in the preferred embodiment of the device lower end 14 of sidewall 12 is flat to provide a stable base when body 11 is placed upon the supporting structure of the stove. If desired, in an alternative embodiment, notches matching the configuration of the horizontal supports of the stove supporting structure could be provided in lower end 14, to be received over the horizontal supports.

A stove burner of the type with which the device of the invention is intended to be used does not, alone, generate sufficiently concentrated temperatures to fire, or sinter, an object formed of metal clay or to fire enamels. The device of the invention serves to concentrate the heat emitted by the burner into a reduced cross-sectional area at the upper end of the body of the device. Since the heat energy resulting from the combustion of fuel at the burner is concentrated at the upper end of the device, an increase in temperature occurs at the upper end of the device, achieving a temperature sufficient for firing objects formed of metal clay or for firing enamels.

The material of construction of the body of the device of the invention is a factor in the ability of the device to constrain the heat energy produced by the burner to within the interior of the body and through the upper end of the device to achieve the necessary temperature at the upper end, or firing zone. The preferred material of construction is an insulating material with very low thermal conductivity, so as to minimize the conduction of heat into the body of the device through the inner surface 15 of sidewall 12 and through the sidewall to the outer surface 16. A finite quantity of heat energy is generated over a given time interval by the stove burner, and the transport of that heat energy from the burner through the hollow interior of the body of the device of the invention is primarily by convection; i.e., the flow of combustion gases. Some heat transport by radiation from the heated burner structure and from the inner surface 15 of sidewall 12 also occurs. Any heat energy that is conducted through sidewall 12 to the exterior of the body, and any heat energy that is accumulated in the material of construction of the body is not available for heating an object to be fired and is effectively lost. Loss of heat energy can result in a failure to achieve the elevated temperature at the upper end of the body of the device necessary for the firing process. The use of a material of construction with low thermal conductivity is also a safety feature. Because very little heat energy is conducted through the sidewall of the body, the temperature of outer surface 16 remains low, and the risk of burns or ignition of materials in contact with the outer surface of the body is substantially eliminated.

A preferred material of construction of body 11 is a refractory ceramic fiber material composed primarily of aluminosilicate. The preferred material has a low density and is of sufficient strength to withstand repeated uses without failure. Appropriate materials for construction of body 11 are commercially available, under various trade names including but not limited to Pyrolite, Pyroboard, and Formcast. It is to be understood, however, that the scope of the invention is not limited to any particular material, and other materials with appropriate properties and characteristics may be used.

Another factor in avoiding heat loss or, conversely, capturing and concentrating the maximum available heat from the burner through the interior of the body of the device is the proportionate cross-sectional dimension, or width, of the body of the device at its base or lower end 14 relative to the width of the flame created at the stove burner. The cross-sectional dimension of body 11 at lower end 14 is sufficiently greater than the width of the flame to assure that the combustion gases, and the heat, from the burner are confined within the interior of the body and not allowed to escape outwardly from the body of the device.

It is desirable that the cross-sectional configuration of body 11 of the device match the configuration of the burner with which it is to be used. The most common burner configuration is circular, and accordingly, effective capture and concentration of heat from a circular burner within the body of the device and the maintenance of a uniform temperature across the firing zone at the upper end of the body is most readily achieved when the cross-sectional configuration of body 11 is also circular. However, the scope of the invention is not limited to any particular configuration, and it is to be understood that other embodiments, in which the cross-sectional configuration of body 11 is polygonal, could be used, although the efficiency and effectiveness of the device may be reduced to at least some degree. For purposes of this description, use of the term “cone” or “conical” in reference to the configuration of the body of the device of the invention is intended to be broadly comprehended, and to include polygonal cross-sectional configurations as well as circular unless otherwise specified.

The proportional relationship between the cross-sectional dimension of body 11 at its upper end relative to the cross-sectional dimension at its lower end, and the relative height of the body of the device between its lower and upper ends is a factor in concentrating heat and achieving the desired temperature at the upper end of the body. In a particularly preferred embodiment body 11 of the device is circular in cross-section, and the inside diameter of the body at upper end 13 is approximately fifty percent of the inside diameter of body 11 at lower end 14. Accordingly, the cross-sectional area of the body at its upper end is approximately twenty-five percent of the cross-sectional area at its lower end. The height of body 11 between its upper and lower ends is approximately sixty percent of the diameter of the body at lower end 14. The angle at which sidewall 12 converges between lower end 14 and upper end 13 is a factor of their respective diameters and the height of body 11. It is preferred that the thickness of sidewall 12 be generally uniform between lower end 14 and upper end 13, although a sidewall of varying thickness is encompassed within the scope of the invention.

The scope of the invention is not limited to these specific proportional relationships, and some variation can be accommodated without unacceptable degradation in performance. More generally, the cross-sectional dimension of upper end 13 relative to lower end 14 may be within the range of about forty percent to about sixty percent, and the height of body 11 relative to the cross-sectional dimension of lower end 14 may be within the range of about fifty percent to about seventy percent. In terms of the corresponding cross-sectional areas, the cross-sectional area of body 11 at its upper end may be within the range of about 0.16 to about 0.36 the cross-sectional area of the body at its lower end. Proportional relationships outside these ranges are also encompassed within the scope of the invention, although performance may be compromised.

A method of firing objects utilizing the device of the invention and a stove having a burner, a supporting structure, and a fuel flow control valve includes the steps of, placing body 11 of the device on the supporting structure of the stove above the burner; generally centering the body over the burner on the supporting structure; inserting temperature sensor 21 through aperture 20 in sidewall 12 and connecting the temperature sensor to a pyrometer assembly 22; placing support screen 19 on ledge 17 at upper end 13 of body 11; placing the object or objects to be fired on support screen 19; lighting the stove burner; monitoring the temperature adjacent to the position of support screen 19 and the object(s) placed thereon; adjusting the temperature as necessary by adjusting the fuel flow control valve; maintaining the desired temperature for the desired duration; and extinguishing the burner.

Fired objects may be removed from support screen 19 immediately following the firing process, which still hot, using a suitable implement, or they may be left on the support screen until cool. During the firing process the outer surface 16 of sidewall 12 remains relatively cool, and can be safely touched without injury.

Any conventional pyrometer assembly that will measure temperatures within the desired range with reasonable accuracy may be used in conjunction with the device of the invention. Although the use of a pyrometer assembly is preferred, objects can be successfully fired without a pyrometer, especially when precise temperature control is not deemed to be necessary. For example, when firing objects formed of metal clay, temperature can be generally discerned by the color of the material, which glows with a dull orange color when heated to the appropriate firing temperature. Nevertheless, more consistent results will be obtained with the use of a pyrometer assembly.

As mentioned above, the device and method of the invention can be very effectively used for firing enameled objects as well as objects formed of metal clay. Typically, enamels are fired in a kiln because temperature control is critical to successful firing. In addition to the disadvantage of the expense of the kiln itself, kiln firing is a lengthy process. The artist is unable to determine whether the firing has been successful until the kiln has cooled sufficiently to be opened, which typically requires several hours. With the device of the invention firing enamels requires only a few minutes of heating time, and the artist is able to not only monitor the complete firing process, but can determine the success or failure of the process immediately.

The foregoing description of the device of the invention and the method of the invention is intended to be illustrative and not limiting. In addition to the certain variations and alternatives described, further variations and alternative embodiments may be devised within the scope of the invention, in accordance with the following claims. 

1. A heat concentrating device for concentrating the heat emitted from a burner for heating objects, the burner having a support structure around the burner, comprising, a body having a continuous sidewall surrounding a hollow interior, with an open first end and an open second end, the cross-sectional area of said open first end being less than the cross-sectional area of said open second end, said body formed of an insulating material of low thermal conductivity, said body to be placed over the burner with said second end upon the support structure around the burner, such that heat emitted from the burner is captured within said hollow interior of said body at said second end and channeled within said interior of said body to and through said open first end, thereby concentrating the heat at said open first end; and supporting means disposed at said first end of said body for supporting objects placed on said supporting means to be heated.
 2. The heat concentrating device of claim 1, wherein said supporting means is a planar screen.
 3. The heat concentrating device of claim 1, wherein said supporting means has a peripheral edge, and wherein said sidewall includes an annular ledge at said first end of said body to receive said peripheral edge of said supporting means.
 4. The heat concentrating device of claim 1, wherein said sidewall is penetrated by an aperture adjacent to said first end of said body, to receive a temperature sensor inserted through said aperture from the exterior of said body to said interior of said body.
 5. The heat concentrating device of claim 1, wherein said material from which said body is formed comprises aluminosilicate.
 6. The heat concentrating device of claim 1, wherein said sidewall has an inner surface and an outer surface, and wherein the thickness of said sidewall between said inner surface and said outer surface is generally uniform between said first end of said body and said second end of said body.
 7. The heat concentrating device of claim 1, wherein said body has a longitudinal axis extending between said first end and said second end, wherein said first end of said body defines a first plane, wherein said second end of said body defines a second plane, and wherein said first plane and said second plane are parallel and mutually perpendicular to said longitudinal axis of said body.
 8. The heat concentrating device of claim 2, wherein said screen is formed of stainless steel.
 9. The heat concentrating device of claim 7, wherein the cross-sectional configuration of said body in a plane perpendicular to said longitudinal axis is circular.
 10. The heat concentrating device of claim 7, wherein the cross-sectional configuration of said body in a plane perpendicular to said longitudinal axis is polygonal.
 11. The heat concentrating device of claim 7, wherein the cross-sectional area of said open first end of said body is about 25 percent of the cross-sectional area of said open second end of said body.
 12. The heat concentrating device of claim 7, wherein the cross-sectional area of said open first end of said body is within the range of about 16 percent to about 36 percent of the cross-sectional area of said open second end of said body.
 13. The heat concentrating device of claim 9, wherein the diameter of said open first end of said body is within the range of about 40 percent to about 60 percent of the diameter of said open second end of said body, and wherein the height of said body between said open first end and said open second end is within the range of about 50 percent to about 70 percent of said diameter of said open second end of said body.
 14. A heat concentrating device for concentrating the heat emitted by a burner for the purpose of firing objects formed of metal clay, objects formed of a combination of metal clay and ceramic beads, and enameled objects, the burner surrounded by a support structure, comprising, a frusto-conical body to be placed over and around the burner on the support structure surrounding the burner, said body formed of an insulating material of low thermal conductivity, said body having a hollow interior, an open first end, an open second end, and a continuous sidewall of generally uniform thickness extending between said first end and said second end surrounding said hollow interior, said first end defining a first plane and said second end defining a second plane parallel to said first plane, the inside diameter of said body at said first end being in the range of about 40 percent to about 60 percent of the diameter of said body at said second end and the height of said body between said first and second ends being in the range of about 50 percent to about 70 percent of said inside diameter of said second end of said body, said body to be placed over the burner with said second end of said body resting upon the support structure around the burner, such that heat emitted from the burner is captured within said hollow interior of said body and channeled within said interior of said body from said second end through said first end, thereby concentrating the heat at said first end; and an object support means removably disposed at said first end of said body for supporting objects to be fired.
 15. The heat concentrating device of claim 14, wherein said sidewall is penetrated by an aperture adjacent to said first end of said body, to receive a temperature sensor inserted through said aperture from the exterior of said body to said interior of said body.
 16. The heat concentrating device of claim 14, wherein said object support means has a peripheral edge portion, wherein said sidewall has an inner surface and an outer surface, and wherein said sidewall includes an annular ledge at said first end of said body, extending from said inner surface of said sidewall toward said outer surface of said sidewall, to receive said peripheral edge portion of said object support means.
 17. The heat concentrating device of claim 14, wherein said object support means is an open mesh screen formed of a material that is non-reactive with the objects to be fired.
 18. The heat concentrating device of claim 14, wherein said insulating material of which said body is formed comprises aluminosilicate.
 19. The heat concentrating device of claim 14, wherein said inside diameter of said body at said first end is approximately 50 percent of said inside diameter of said body at said second end, and wherein said height of said body between said first end and said second end is approximately 60 percent of said inside diameter of said body at said second end.
 20. A method of firing objects formed of metal clay, objects formed of a combination of metal clay and ceramic beads, and enameled objects, utilizing an adjustable gas fueled burner having a support structure around the burner, comprising the steps of, placing upon the support structure and generally centering above the burner a heat concentrating device having a frusto-conical body formed of an insulating material of low thermal conductivity, said body having a hollow interior, an open first end, an open second end, and a continuous sidewall penetrated by an aperture adjacent to said first end of said body to receive a temperature sensor therethrough, the diameter of said body at said first end being substantially less than the diameter of said body at said second end, and the diameter of said body at said second end being larger than the burner such that said second end of said body extends outwardly beyond the burner; inserting a temperature sensor through said aperture in said sidewall and connecting said temperature sensor to a pyrometer; placing an object support screen across said first end of said body of said heat concentrating device; placing the object or objects to be fired on said object support screen above said hollow interior of said body of said heat concentrating device; igniting the burner so as to produce heat from the combustion of fuel, whereupon the heat produced by the burner flows upward into said hollow interior of said body of said heat concentrating device through said second end thereof, through said interior, and through said first end, thereby concentrating the heat and exposing the objects placed at said first end of said body to the concentrated heat; monitoring the temperature adjacent to said first end of said body of said heat concentrating device measured by said temperature sensor and said pyrometer; adjusting the burner to achieve and maintain the temperature desired for firing the objects placed on said support screen; continuing operation of the burner for the time appropriate for the firing of the objects placed upon said support screen; and extinguishing the burner upon completion of the firing of the objects. 